As a result of ¡§the X-ray Phase Problem¡¨, traditional direct methods can¡¦t solve the structures of the large molecules. For exploring alternate methods, Wu-Pei Su applied simulated annealing to solve the structure of the large molecules and obtained success. Adopting his concept, we wrote a program for solving the structure of the molecules by C Program Language. And for decreasing the running time of the program, we introduced the concept of genetic algorithm into simulated annealing method.

In recent years, there has been increasing demands for high dielectric materials to replace SiO2 for high-density dynamic random access memories with ultra large scale integration (ULSI). As the dimensions of the charge storage node decrease in high-density dynamic random access memories (DRAMs), TiO2 and BaTiO3 are very promising candidates for applications with exhibiting higher dielectric constant, high refractive index and high chemical stability. The growth of TiO2 and BaTiO3 thin films on various substrates i.e. (100) silicon¡B(100) GaAs¡B(100) InP and (100) MgO are studied by MOCVD using Ti(i-OC3H7)4, Ba(DPM)2, N2O and O2 as precursors. The growth was performed in a cold wall horizontal system in the temperature range of 280~750¢J. The growth rates and structure of TiO2 and BaTiO3 films are affected by the substrate temperature and reactor pressure, etc. The phase transition properties of TiO2 were studied via X-ray diffraction measurements. X-ray diffraction examination shows that phase transition of TiO2 films are at the same temperature of 450 oC on different substrates. Phase-pure rutile is obtained down to 450¢J on InP (100) and GaAs (100), while phase-pure anatase is obtained up to 450¢Jon MgO (100). The optical and electrical properties are associated with the film structures. TiO2 single phase films with rutile (110) orientation were successfully grown on InP (100) at 500¢J. In-plane epitaxial relationship of anatase TiO2 (100) // MgO (100) is present between 300¢J and 375¢J. In addition, the influences of substrate temperature and oxidizer on the structural and electrical properties of BaTiO3 films will be also studied. However, TiO2 and BaTiO3 films have columnar structures acted the paths of leakage current resulting low dielectric constant. We use thermal annealing to improve the quality of TiO2 with respect to leakage current density and dielectric constant. Dielectric constants of annealed TiO2 films were as high as 110.08. Leakage current density reduced to 5 ¡Ñ 10-5 A/cm2. In the future, to improve the crystal structure of the films is the goal in our study.

On account of ¡§the X-ray Phase Problem¡¨, it¡¦s impossible to get the electronic density by inverse Fourier transformation(IFT). And the crystal structure of molecule can¡¦t be solved by IFT. There are many methods to overcome the problem, such as Direct Method, Heavy Atom, and Simulated Annealing. But for macro-molecules, we still face a great challenge due to tremendous computing load. We propose a method by using wavelets to resolve the electronic density. We hope the multiresolution nature of wavelets can reduce the computing load for simulated annealing method.

The £\-helix structure of protein is very similar to the cylindrical structure. Especially, the Sperm-Whale Myoglobin molecules has 70% £\-helix structure. Therefore, we use simulated annealing method to solve ¡§X-ray phase problem¡¨, and apply Metropolis algorithm to avoid local minimum. We hope that the new method can build £\-helix structure of Sperm-Whale Myoglobin molecule. Therefore, we use multi cylinders as the Myoglobin¡¦s tertiary structure and solve the cylinder¡¦s structure with the simulated annealing method.

Thesis (Ph. D.)--York University, 2001. / Typescript. Includes bibliographical references (leaves 107-115). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ67907.

Zugl.: Kassel, Univ., Diss., 2007

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published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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